The invention relates in general to tube-launched projectiles and in particular to obturators for tube-launched projectiles.
An obturator may be used with a tube-launched projectile to seal propellant gas behind the obturator. In rifled launch tubes, the obturator may also function as a torque or spin regulating device to regulate the amount of spin transferred from the obturator to the projectile.
U.S. Pat. No. 6,085,660 issued on Jul. 11, 2000 to Campoli et al. discloses a low spin sabot having a slip obturator with ports to help reduce the spin rate of tank ammunition. U.S. Pat. No. 4,109,582 issued to Haep et al. on Aug. 29, 1978 discloses twist-reducing rings for stabilized projectiles. U.S. Pat. No. 5,164,540 issued to Chiarelli et al. on Nov. 17, 1992 discloses a slipping driving band for projectiles of any caliber. A slip obturator made of composite material has been used with the M712 Copperhead projectile. A discarding slip obturator made of polyetheretherketone (PEEK) has been used with the M982 Excalibur projectile.
Some projectiles (e.g., 155 mm artillery projectiles) are “hard” loaded from the breech end of a launching tube by ramming the projectile into the forcing cone area of the tube. When the projectile is rammed into the forcing cone area, the obturator on the projectile is deformed by mechanical interference with the forcing cone surface. The propellant is placed behind the projectile and the breech is closed. Other projectiles (e.g., 105 mm projectiles) may use a different, so-called “soft” loading procedure.
The soft loading procedure uses semi-fixed ammunition. Semi-fixed ammunition is manually prepared by placing propellant in a cartridge case and then placing a projectile on the cartridge case. The gunner than manually chambers the projectile and cartridge case in the breech of the launch tube by pushing on the base of the cartridge case with his/her fist, thereby sliding the projectile into the forcing cone area. Manually sliding the projectile into the forcing cone area produces little or no mechanical interference between the projectile's obturator and the forcing cone surface. Then, the slightly tapered breech closure slides upward and locks into place, thereby setting the cartridge case and projectile. In some cases, it may be difficult to close the breech because the projectile will not move forward sufficiently into the forcing cone area.
Among other factors, the amount of mechanical interference between the obturator and the forcing cone surface determines the amount of initial propellant gas blow-by past the obturator. The initial gas blow-by for a soft loaded projectile is greater than for a hard loaded projectile and is difficult to control. The greater blow-by causes, among other things, loss of propellant gas pressure and excessive heat and pressure applied to areas of the round forward of the obturator.
The amount of mechanical interference between the obturator and the projectile is also important. When the projectile is fired and moves forward through the forcing cone area, mechanical interference between the obturator and the forcing cone surface tends to swage the inner surface of the obturator onto the outer surface of the projectile. The swaging of the obturator to the projectile imparts torque and spin to the projectile. However, for precision guided munitions that are fin-stabilized, high spin rates may be undesirable.
A need exists for an efficient obturator for a soft loaded 105 mm projectile that enables ease of loading of the projectile in the gun, reduces initial blow-by and imparts reduced torque to the projectile.